The invention relates to a plant for dynamically manufacturing and for packaging medical gas mixtures, particularly N2O/O2 gas mixtures that can be used in the medical field, especially in analgesia, preferably N2O/O2 mixtures containing approximately 50 vol % nitrous oxide (N2O) and 50 vol % oxygen.
From the industrial standpoint, there are at the present time various methods and processes for manufacturing and packaging gas mixtures.
However, in these the amounts of gas to be mixed are fed into a gas mixer and are monitored by measuring the pressure and the temperature of the gases. The metering is therefore based on two measuring instruments which add their measurement errors, thus possibly leading to quite random results.
Moreover, the choice of measurement points in the plant does not allow the desired physical quantities to be determined, or does so only incompletely, and therefore does not allow the mixture to be produced effectively or reliably.
Thus, the temperature is usually measured at the gas-filling injection rail by a temperature probe which does not reflect, or does so only very inaccurately, the effective gas temperature in the packaging containers.
Sometimes this measurement is performed directly on the surface of the container (bottle) by an infrared thermal probe; it will be understood that this measurement is not a precise reflection of that of the gas in the container.
Moreover, a pressure sensor is used to constantly measure the pressure in the filling injection rails, the gases while flow through the pipes.
Consequently, there is therefore an inevitable difference between the final pressure in the containers, at the end of filling, and the pressure measured during filling, which depends on the pressure drops, the flow rate and the temperature of the gases.
Not knowing the pressure-drop coefficients and the temperature of the gases precisely therefore requires the pressure to be checked in static mode, at the end of the injection cycle, that is to say a posteriori.
Thus, if the amounts of gas mixed are off-specification, it is then necessary to top up the amounts of gas mixed by adding the amount of gas lacking, something which is not practical or not always easily achievable.
However, conversely, any excess gas completely falsifies the precision of the desired gas mixture and either results in the gas mixture thus obtained being scrapped or requires a readjustment in order to try to re-establish the equilibrium. This is not always possible.
Furthermore, a process for packaging gas mixtures based on carbon dioxide (CO2) is also known, this process being called a dynamic packaging process, in which the CO2 is packaged above a supercritical state at a pressure of 270 bar and at a temperature between about 70xc2x0 C. and 120xc2x0 C., both the pressure and the temperature of the gas being determined by the conditions under which the packaging process is carried out.
The pressures of the various gas sources must be balanced at 270 bar since the pressure is defined in such a way that containers can be filled at a pressure of 200 bar even in summer when they are hot, since they are usually stored outdoors. This means that the filling source downstream of the mixing chamber must therefore be able to reach 240 bar (for a container at a temperature ranging up to 60xc2x0 C.).
In addition, the pressure drops across such a dynamic mixer often reaches 20 bar and consequently the pressures of the gas sources must reach a minimum of 260 bar.
Hitherto, CO2 is the only liquefied gas that has already been packaged dynamically.
During a filling cycle, the pressures of the gas sources are reduced downstream of the mixing chamber down to the pressure of the containers and the pressure downstream of the chamber varies, during the cycle, from a few mbar to the final filling pressure of the gas mixture.
In the case of CO2 at a pressure of 270 bar, the temperature is 70xc2x0 C. and this is chosen so that the expansion is not accompanied by a change of state of the CO2, passing into the solid state (carbon dioxide snow) especially when the pressure is less than 5 bar.
This is because any formation of carbon dioxide snow runs the risk of obstructing the taps of the bottles, thus resulting in disparities in the contents of the gas mixtures produced in the bottles for the same filling injection rail.
Consequently, only gas mixtures containing a CO2 content generally not exceeding 30% can be produced, since otherwise the temperature reached downstream of the expansion chamber would be below the demixing temperature.
Gas mixtures whose content of a given component is greater than 30% (by volume) are usually produced by more conventional manufacturing methods, for example by gravimetry with a check of the masses injected into the bottles by weighing or by a temperature-corrected pressure measurement. However, these methods have the drawbacks of making it almost mandatory to roll the bottles after mixing in order to homogenize the contents thereof and to carry out an analytical check on the containers in order to ensure that they conform to the intended specifications. Such procedures are therefore not very practical and are expensive in terms of time and of productivity.
Furthermore, during dynamic mixing there is also the problem of demixing of the gas mixture downstream of the mixing chamber, that is to say inopportune demixing or separation of the various components of the mixture downstream of the site where the said mixing takes place.
Demixing of a gas mixture is characterized by the separation of the said mixture into two separate phases, namely a gas phase and a liquid phase.
Demixing occurs as soon as the temperature of the mixture drops below a temperature threshold. The higher the gas content of the mixture the higher the demixing temperature.
For a binary gas mixture formed from 50% O2 and 50% N2O, this demixing threshold is about xe2x88x925.5xc2x0 C., as explained in the document xe2x80x9cEquilibria for mixtures of oxygen with nitrous oxide and carbon dioxide and their relevance to the storage of N2O/O2 cylinders for use in analgesiaxe2x80x9d, March 1970.
Now, gas packaging using a dynamic mixer is always accompanied by an expansion downstream of the mixing chamber and therefore in general a reduction in the temperature of the gases, even to below the demixing temperature in the case of an analgesic mixture.
The flow of the gases through the filling injection rails into the bottles is therefore a two-phase flow, the liquid phase and the gas phase moving at different flow velocities.
Consequently, the bottles are no longer filled homogeneously and relatively large differences are observed in the final contents of the mixtures produced in each of the bottles filled from the same injection rail during the same manufacturing cycle or process.
These disparities may be explained by preferential flows of certain constituents of the gas mixture with respect to others in the pipes of the injection rails for filling the containers, namely gravitational flows or flows in the form of droplets in the case of liquefied gases.
Thus, under high filling-rate conditions or in the case of type B5 small-volume (5 liter) containers, the resulting contents of mixtures in a few containers of the same manufacturing batch may be outside the production tolerances imposed by the Pharmacopoeia, namely a maximum deviation of 1% in the case of a 50 vol %/50 vol % O2/N2O mixture. Consequently, it is essential to carry out an analytical check on each container. This is tiresome and not very practical from the industrial standpoint.
Thus, it is an object of the present invention to be able to produce gas mixtures, in particular gas mixtures intended for the medical field, and then to package them rapidly, reliably and effectively, that is to say without encountering the problems that arise with the conventional packaging processes.
Put another way, the problem that arises is to be able to produce and package, dynamically, gases for producing gas mixtures containing mainly one or several of the following constituents O2, CO2, N2, He and N2O in predefined proportions so as to allow the production of mixtures having a variable content of a given gas, especially CO2 and N2O in contents greater than 30%, in particular a process that can be used for producing medical gas mixtures, for example 50 vol %/50 vol % oxygen/nitrous oxide analgesic binary gas mixtures, while preventing the gas mixture thus produced from reaching its demixing temperature threshold or point.
In other words, the process of the invention should have the advantages of the known CO2 dynamic packaging process without having its drawbacks, that is to say to be able to be used to manufacture gas mixtures having, in particular, a content of more than 30% of a given gas, such as nitrous oxide (N2O) or oxygen, while minimizing or preventing as far as possible the demixing phenomenon.
It follows that the solution provided by the present invention relies on a process for manufacturing gas mixtures containing at least a first component and at least a second component in predefined proportions, the said first and second components being chosen from the group formed by O2, N2, He and N2O, in which:
(a) predetermined proportions of at least the said first component and the said second component are mixed dynamically in order to obtain a gas mixture of the desired composition;
(b) the temperature of the said gas mixture containing the said first and second components obtained in step (a) is adjusted in order to keep it above the demixing threshold temperature of the said mixture.
According to another aspect, the invention also relates to a process for manufacturing gas mixtures containing at least a first component and at least a second component in predefined proportions, the said first component being chosen from the group formed by O2, N2, He and N2O and the said second component being CO2, in which:
(a) predetermined proportions of at least the said first component and the said second component are mixed dynamically in order to obtain a gas mixture of the desired composition;
(b) the temperature of the said gas mixture containing the said first and second components obtained in step (a) is adjusted in order to keep it above the demixing threshold temperature of the said mixture.
Depending on the case, the manufacturing process of the invention may include one or more of the following characteristics:
the second component is chosen from CO2 and N2O and the content of the second component (N2O or CO2) is greater than or equal to 30 vol %, preferably at least 40 vol %;
the first component is oxygen and the second component is nitrous oxide (N2O) and preferably the gas mixture consists of 50 vol % of the said first component and 50 vol % of the said second component, the first component being oxygen and the second component being nitrous oxide (N2O);
at least one of the said first and second components is in the supercritical state;
in step (b), the temperature of the gas mixture is adjusted to or kept above xe2x88x925.5xc2x0 C.;
the temperature of the gas mixture is adjusted by warming the gas mixture by heat exchange, preferably the said warming being carried out by at least one electric heater;
the gas mixture contains CO2 and O2, and possibly helium;
the pressure of the gas mixture is between 120 bar and 300 bar;
at least a first component and at least a second component in predefined proportions in at least one container, particularly a gas bottle, the said gas mixture being obtained by a gas mixture manufacturing process;
a gas mixture consisting of 50 vol % oxygen and 50 vol % nitrous oxide (N2O) in at least one container, in particular a gas bottle, the said gas mixture being obtained by a gas mixture manufacturing process.
The invention also relates to a plant for manufacturing, dynamically, gas mixtures containing at least a first component and at least a second component in predefined proportions, comprising:
a source of the first component, containing the said first component;
a source of the second component, containing the said second component;
at least one dynamic mixing chamber for mixing the said first and second components in order to obtain a gas mixture of the desired composition; and
temperature adjustment means located downstream of the said mixing chamber allowing the temperature of the said gas mixture containing the said first and second components to be adjusted or kept above the demixing threshold temperature of the said gas mixture.
Preferably, the plant may include one or more of the following characteristics:
the temperature adjustment means are chosen from heat exchangers and preferably electric heaters;
compression means located upstream of the said chamber, warming means located upstream of the said chamber and/or at least one buffer tank, the plant preferably having the compression means, the warming means and the buffer tank placed in series;
control means acting on the compression means in response to a predetermined pressure threshold being detected by at least one pressure sensor designed to be able to determine the pressure obtaining in the said buffer tank.
According to yet another aspect, the invention relates to a plant for filling containers with gas, which comprises:
a manufacturing plant; and
conveying and filling means located downstream of the temperature adjustment means and making it possible to convey the gas mixture to at least one gas container to be filled with the said gas mixture and to fill the said container.
Within the context of the present invention, xe2x80x9cdynamic mixingxe2x80x9d is understood to mean mixing carried out by continuous and/or simultaneous injection of the constituents of the said mixture into a mixing chamber and/or direct injection into packaging containers, and this being achieved with the expected or desired final composition.
The various problems encountered with the conventional packaging processes do not in fact arise with a dynamic mixer according to the invention, this being so for several reasons, and, above all, because the metering of the masses by a mass flowmeter obviates the uncertainties in the temperature and pressure measurements, and the manufacturing vagaries associated with the errors on the measured amounts and values which exist with the said known packaging processes.
The xe2x80x9cdynamicxe2x80x9d gas mixture packaging process according to the invention is particularly suitable for the production and packaging of gas mixtures intended for use in the medical or pharmaceutical field, which gas mixtures must meet strict requirements in terms of mixture quality and precision, especially for obvious reasons of patient safety.
The dynamic packaging method of the invention is particularly suitable for the manufacture of gas mixtures based on O2, N2, He and N2O, or even CO2 but with a volume content greater than 30%.
The dynamic packaging process, also called dynamic mixing, consists in filling, from the start to the end of the packaging sequence, one or more gas bottles with a gas mixture having the desired final composition.
The gas mixture is produced upstream of the filling injection rail in a very small mixing chamber into which the gases making up the composition of the mixture to be produced are fed, the amounts fed for each gas being monitored by a mass flowmeter assigned to each source of each of the constituents of the gas mixture to be produced.
A set of several control valves is used to control the source gas flow rate by virtue of the action of an automatic control system.
In general, the dynamic packaging process of the invention has the following main advantages:
the packaged mixture is immediately homogeneous, that is to say it does not require the bottles to be subsequently rolled in order to mix and properly homogenize the gases which are in them;
it makes it possible to limit the production variations in the content for a bank of bottles filled during the same filling cycle given that the batch manufactured may be qualified by a single analysis carried out on one bottle of the batch, thus resulting in savings being made both in the cost of analytical testing and in filling time;
mass-based metering of the amounts of gas to be packaged has the advantage of providing measurement accuracy and therefore of metering the amount on each source gas irrespective of the pressure and temperature conditions. The accuracy of mass-based metering therefore makes it possible to achieve an extremely low level of gas mixtures which are scrapped after analytical testing; and
the fact of carrying out mass-based metering rather than measuring pressures and temperatures has the advantage of avoiding the measurement errors that can occur in gas mixtures and therefore of solving the problem of obtaining gas mixtures whose contents of the various components of which they are composed do not conform to the desired contents.
In addition, by virtue of the process of the invention, the contents of the various constituents of the said gas mixture within several containers filled during the same filling cycle are reproducible from one container to another, that is to say from gas bottle to gas bottle, since the manufacturing deviations are extremely small from one bottle to another. Consequently, a batch of several bottles filled during the same filling cycle may be checked by analysing a single bottle taken at random from the batch and it is no longer necessary to repeat this check on several bottles, as is usually the case. This makes it possible to save time and to increase the productivity and efficiency of the packaging process.
In other words, a very high level of packaging reproducibility is achieved over time by using a dynamic mixer for packaging gas mixtures, in particular N2O/O2 gas mixtures.